It is well known that blends of elastomers such as acrylonitrile-butadiene copolymers (NBR) containing polar groups are not compatible with hydrocarbon rubbers such as ethylene-propylene rubbers. It is possible, however, to blend nitrile rubbers with certain polar resins such as styrene acrylonitrile; see for example U.S. Pat. No. 2,439,202. Blends of nitrile rubbers with acrylonitrile/butadiene/styrene resins have been prepared; see for example Japanese Pat. No. S-7-5013369. These blends have also been prepared incorporating a third component such as polyvinylchloride; see for example U.S. Pat. No. 3,629,050.
Graft polymers of ethylene propylene terpolymers wherein the third monomer is a non-conjugated diene (EPDM) have been prepared wherein the graft polymer comprises styrene acrylonitrile resins (SAN). These grafts of SAN on an EPDM backbone are known as EPAS. EPAS has been successfully blended with SAN to prepare weather resistant, impact resistant resins; see for example U.S. Pat. Nos. 3,489,821 and 3,489,822.
NBR has good solvent resistance but poor ozone resistance and heat aging properties. The poor qualities are believed to be the result of sites of unsaturation in the backbone which permits scission of the polymer chain to occur under certain adverse conditions. EPDM, on the other hand has good heat aging and ozone resistance because its unsaturation sites are in side chains which render the polymer generally immune to scission of the backbone chain. However, these hydrocarbon rubbers have poor solvent resistance even in the cured state.
It has been postulated that blends of EPDM and NBR would exhibit a desirable balance of heat, ozone and solvent resistance. However, these rubbers are incompatible, and blends thereof are not homogeneous. Consequently, they have poor physical properties such as tensile, modulus, elongation and tear strength and have little practical value.